The present invention relates generally to optical disks, such as CDs (Compact Disks) and DVDs (Digital Versatile Disks), and optical disk reproduction systems, and more particularly to an improved method of recording TOC (Table-OF-Contents) information on an optical disk.
In optical disks such as CDs (Compact Disks), TOC (Table-OF-Contents) information is used to make instantaneous access to a start point of a designated recording track. It has been conventional to record such TOC information as subcodes in a lead-in area of the disk. Specifically, as shown FIG. 11. the optical disks generally include a lead-in area LIA disposed along its inner periphery, a lead-out area LOA disposed along its outer periphery, and a program area PGA located in between the lead-in area LIA and the lead-out area LOA. These three areas each contain recording units called "EFM (Eight to Fourteen Modulation)" frames. Each of the EFM frames, as illustratively shown in FIG. 12, includes a synchronizing bit, a subcode (one symbol), data (12 symbols), P parity bits (four symbols), data (12 symbols) and Q parity bits (four symbols), and the 12-symbol data and P and Q parity bits constitute data of a main channel. Thus, each of the EFM frames of the optical disk contains a total of 33 symbols in the main channel and subcode channel: 32 symbols in the main channel; and one symbol in the subcode channel. Because each of the symbols consists of "14+3" bits and "24+3" bits are used as the synchronizing bit, each of the EFM frames has a total length of "24+3+(14+3).times.33" (=588) bits. The subcodes of 98 such EFM frames together constitute a single subcode block that represents a single unity of information, and TOC (Table-OF-Contents) information is recorded in the subcode block of the lead-in area LIA.
FIG. 13 shows one of the subcode blocks in the lead-in area LIA. The subcode in each of the EFM frames is EFM-decoded into one-byte or eight-bit data, and unique channel names "P" to "W" are allocated respectively to the eight bits of the decoded subcode. The subcodes of the first two EFM frames are called "S0" and "S1" codes, which are used as a synchronizing signal. A group of the subcodes of channel Q in 96 EFM frames is commonly called a "subcode frame", and this subcode frame represents positional information of a track. In the subcode frame consisting of 96 Q-channel bits, bits Q1 to Q4 represent a data/audio flag, bits Q5 to Q8 represent an address, bits Q9 to Q16 represent a track number, bits Q17 to Q24 a start point, and bits Q25 to Q48 represent a relative position TIME of the subcode frame in the lead-in area LIA; the relative position data TIME comprises a set of three data MIN, SEC and FRAME indicative of minute, second and frame, respectively. Further, of the 96 Q-channel bits, bits Q57 to Q80 represent an absolute position PTIME of a track corresponding to a track number specified by the above-mentioned start point, the absolute position data PTIME comprises a set of data PMIN, PSEC and PFRAME. Last 16 bits Q81 to Q96 represent a CRC (Cyclic Redundancy Check) code to be used for error detection.
A plurality of such subcode frames arranged in the aforementioned manner together constitute TOC information as illustratively shown in FIG. 14. The TOC information indicates respective track numbers and start points of all of the tracks provided in the program area PGA. Because the subcodes themselves do not have error correcting capability, the same start point information of each one of the tracks is recorded repetitively three times in succession. Similarly, a same set of three types of control information, i.e., control information A0 (indicative of the leading or forefront track number, a type of the disk, etc.), control information A1 (indicative of the last track number) and control information A2 (indicative of a total recording time period), are recorded repetitively three times in succession in an end portion (corresponding to frame numbers "n+m" to "n+m+8" in the illustrated example) of the TOC information. Such TOC information is recorded repetitively in the lead-in area.
Today, the number of tracks recordable in the program area PGA differs depending on the type of the optical disk; the smallest number is just one while the greatest number is 99. Thus, the maximum number of subcode frames necessary for recording TOC information will be EQU [99 (the number of the recordable tracks)+3 (the number of the types of the control information)].times.3=306 Mathematical Expression (1)
In the CDs (Compact Disks), 75 frames correspond to a time length of one second and it will take 1/75 (=0.0133) seconds to read out a single subcode frame at the normal replay speed. Thus, with the CD having the greatest number of, i.e., 99 recordable tracks, it would take as long a time as 4 seconds to completely read out the TOC information.
Further, although read errors may be detected by use of the CRC code in the subcode frame, the subcode frame does not have error correcting capability. Thus, when some read error is detected, next one of the repetitively recorded TOC information has to be re-read, which would require an even longer readout time.